Guy left play group playing in a tree (6)
I believe the answer is:
poplar
'tree' is the definition.
(poplar is a kind of tree)
'guy left play group playing' is the wordplay.
'left' suggests deleting specific letters.
'playing' is an anagram indicator.
'play'+'group'='playgroup'
'playgroup' with 'guy' removed is 'plarop'.
'plarop' is an anagram of 'POPLAR'.
'in a' acts as a link.
(Other definitions for poplar that I've seen before include "Tree - London district" , "Tree as tulip-tree, aspen" , "Tree with leaves that quiver" , "Tree of north temperate regions, with flowers borne in catkins" , "Tree with light, soft wood and catkins" .)